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Why there are Universal Donors and Universal Recipients

“Universal donor” and “universal recipient” are terms used in discussing blood transfusions to refer to people who are capable of giving blood to anyone else, and people who are capable of receiving blood from anyone else, respectively. The capacity to universally donate or universally receive blood is a result of the relationships between different blood types.

In most cases, great care must be taken before arranging to give blood from one person to another as part of a medical or emergency procedure. The reason for this is that humans have different blood types. First, there are four general blood types, identified by the presence of certain genetically determined substances called antigens on their red blood cells: blood type A (people who have the A antigen in their blood), blood type B (the B antigen), type AB (both antigens), and type O (neither antigen).

Blood is then subdivided further into whether it carries a separate antigen, Rh. Someone who has the Rh antigen and is blood type A can thus be referred to as “type A-positive,” while an otherwise identical person without the Rh antigen would be “type A-negative.” There are also a number of other antigens determining additional blood group subsets which may be important in some cases. For example, the Duffy antigen is seldom present in white patients, but often present in African or African-American patients.

Blood type determination is now a routine and very simple test and normally carries no medical significance, but carries important medical consequences. Patients who are given blood must be given blood of a type compatible with their own. If blood containing an antigen is given to a person who does not already carry the antigen, their immune system is likely to identify the new blood as a threat, manufacture antibodies against it, and potentially cause a serious or even life-threatening reaction. Essentially, humans are severely allergic to blood of incompatible types.

However, blood matching is not as simple as finding someone of exactly the same blood type. Because the immune reaction is to an antigen not already present, a person who is Type A-positive can receive a blood transfusion from a donor who is Type O-negative, because they will not be receiving any antigens which they are not familiar. However, a person who is Type A-negative and receives blood from a Type A-positive donor is at risk of reacting to the unfamiliar Rh antigen.

The terms universal donor and universal recipient refer to people who, because of their blood type, are capable of receiving or giving blood in any circumstance. Universal donors are Type O-negative people; because they have no antigens with which anybody else’s immune system would be unfamiliar, their blood can be donated to any patient. According to the Red Cross, there are very few universal donors: just 7% of Caucasians, 4% of African-Americans, and 1% of people of Asian descent.

In the same way, universal recipients are people whose immune systems have already accepted all blood antigens, and therefore can receive blood from anybody else regardless of blood type. Universal recipients are Type AB-positive; that is, they already carry the A antigen, the B antigen, and the Rh antigen. According to the Red Cross, universal recipients are roughly as rare as universal donors: 3% of Caucasians, 4% of African-Americans, and 7% of people of Asian descent.